1. Field of the Invention
The present invention relates to a stepping motor used as a driving source for stepping movement of automatic-machine members.
2. Description of the Related Art
Though a stepping motor using a magnet rotor is already known in the art, it has disadvantages of small output torque and stepping speed.
When increasing the output torque, the stepping speed decreases. To perform the specified operation stepping at a high speed without outstepping, the prior art slowly increases the frequency of the stepping electric signal and slowly decreases it to step. However, the prior art has many problems including that the electric circuit is complicated and expensive and it is difficult to obtain a satisfactory performance.
For one stepping operation, one exciting coil is turned off, the accumulated magnetic energy is discharged, and magnetic energy is accumulated when the next exciting coil is turned on. Discharge and accumulation of the magnetic energy requires time. For a large output torque, the stepping time increases and high-speed stepping is impossible because large magnetic energy is accumulated.
To avoid the above-mentioned disadvantage, means is provided to execute high-speed stepping by raising the applied voltage to quickly accumulate magnetic energy and returning the accumulated magnetic energy to the power source to quickly decrease it. However, the means has the following two disadvantages. First, the means cannot be used under a low voltage because the applied voltage is too high.
Secondly, because the means is limited to high-speed stepping, it is impossible to achieve a higher-speed stepping operation.